someone who performs rap music
"The local rapper dropped a new track last night that had everyone dancing in the club."
a device (usually metal and ornamental) attached by a hinge to a door
"The heavy brass rapper on the old cabinet door has developed a loose hinge that lets it swing freely when I open it."
One who, or that which, raps or knocks.
"The old house had a loose floorboard where every step by the cat sounded like a rhythmic rap against the wood above."
The knocker of a door.
"The loud banging on my apartment door made me wonder if someone was just trying to use their foot as a makeshift rapper."